1. Field of the Invention
The present invention relates to seek control technology, and in particular to a seek control method for a disk device used for reading/writing data from and to a disk recording medium, such as a compact disk (CD) or a compact disk-read only memory (CD-ROM).
2. Description of the Related Art
In a disk device, such as a CD-ROM drive, a seek control operation is performed by calculating the number of tracks a pickup has to pass to reach the target track from the present track, and moving the pickup until the number of tracks passed equals the number of tracks calculated.
A generally well known seek method, which includes the step of calculating the number of tracks the pickup passes, is a track zero cross detection seek. The track zero cross detection seek is a seek method which samples a zero cross point or an arbitrary point on the disk for determining when the disk has made one complete revolution. The zero cross point is sampled by detecting a tracking error signal as the pickup moves in a radial direction of the disk and zero crossing the tracking error signal with a desired reference voltage. Every time the zero point is sampled, mirror signals are generated and counted by a CPU, where each mirror signal represents one track in a track pitch direction for every associated period of time. Accordingly, the pickup is moved until the counted number of mirror signals is equal to the calculated number of passing tracks required to reach the target track.
Although the track zero cross detection seek is especially advantageous in seeking the target track, even in a high rate of disk revolution, the operation sometimes misses the mirror signals. For example, if the disk has defects, such as a crack, fingerprints, dust, or stains, the tracking error signal may not be zero crossed with the desired reference voltage, thereby resulting in missing mirror signals. Further, even though there may not be any defects, mirror signals may still be missed due to the occurrence of a servo error, such as the occurrence of a focus drop which may be generated during the seek operation. The servo error may cause a miscount between the counted number of mirror signals and the number of actually passed tracks, thereby causing an inaccurate seek operation.
Accordingly, a need exists for a seek control method which accurately moves a pickup to a target track even when mirror signals are missed or miscounted during a seek operation.